Definition
Plain language
A table of how strongly every item in a set lines up with every other item.
As stated in the literature
A matrix of pairwise inner products over a set of vectors; in Echo and SKA it accumulates as a streaming sufficient statistic enabling closed-form ridge-regression retrieval.
Why it matters: It compactly stores all the pairwise relationships a system needs, letting it answer queries with fast, exact math instead of redoing comparisons.
For example, given a handful of documents, it records how similar each one is to every other, filling a grid of those pairwise comparisons.
Heard on the show
“The first is the Gram matrix of keys — a running table of dot products between all the keys you've seen.”Episode 033 — Echo: The Paper Arguing You Never Needed a KV Cache for Retrieval